Electrically insulating pipe section for high-vacuum pipe lines



W. DLLENBACH ELECTRIGALLY INSULATINGQRIPE SECTION FOR HIGH VACUUM PIPE LINES Q Filed July 51, 1922 fare/fior" Patented Nov. 18, 1924.

UNITED STATES PATENT OFFICE.

WALTER DLLENBACH, OF BADEN, SWITZERLAND, ASSIGNOR TO AI['{TIE].\T(5r1 1fSEI.|ll2r SCHAFT BROWN, BOVERIAND CIE.7 OF BADEN, SWITZERLAND.

ELECTRICALLY INSULATING PIPE SECTION FOR HIGH-VACUUM PIPE LINES.

Application filed July 31, 1922.

To all whom t may concern:

Be it known that I, WALTER DLLENBACH, a citizen of the Swiss Republic, residing at No. 23 Dynamostr., Baden, Switzerland, have invented certain new and useful Improvements in Electrically Insulating Pipe Sections for High-Vacuum Pipe Lines, of which the following is a specification.

This invention has for its object tol provide an improved electrically insulating pipe section for high-vacuum pipe lines, which is of great value for insulating pipe lines electrically from one anotherl in highvacuum installations, especially in those cases where a portion of the high-vacuum installation is under high electrica-l pressure, whilst the other portion is required to be continually accessible Vfor inspection. This is, for instance, the case,l in large rectifier installations where the large rectifier is connected to a high-vacuum pump by pipe lines which convey the high direct current potential of the rectifier to the highvacuum pump, so that the latter must be so mounted as to be insulated from vearth 'for the fullv direct current voltage. One way of carrying the invention into effect willY now be described with reference to the accompanying drawings, in whichl Figure l shows an ordinary insulating pipe section;

Figure 2 is a curve connecting breakdown voltage with the product of gas pressure and length of spark gap;

Figure 3 shows a portion of the insulation section Iof a vacuum pipe with a perforated metal screen inserted across the passage;

Figure t is a section of a vacuum pipe having an insulated portion according to the invention.

A simple expedient would consist, as shown in Fig. l, in insulating the dierent parts t and b of the installation from each other by the interposition of a pipe section c composed of insulating material. This eX- pedient is effective so long as a high-vacuum actually exists in the pipe line. But immediately the vacuum deteriorates, the socalled sparking voltage, that is, the voltage required Jfor striking across, will at first diminish, and may fall below the direct current voltage of the rectifier. If that case should occur, then the spark strikes across, inside the insulating section, in the form of a passing-through arc which raises Serial No. 578,734.

the 'pumping plant to the potential of the rectifier, and thereby endangers the said pumping plant.

On a further rise of pressure the sparking voltage increases again, but the arc, when it has been once formed, continues even when the pressure continues to rise. The curve of the sparking voltage has the shape shown in Fig. 2. In this figure V is the sparking voltage. This latter is plotted as a function of the product 29.00, where p is the gas pressure, and x is the distance between the electrodes (in the present case, the length of the insulating section) As will be perceived 'from Fig. 2, there is a critical value of 29.50 at which the sparking voltage is a minimum. In normal working, the installation works below the value par (crit), so that when the vacuum deteriorates, the sparking voltage at first tends to assume its minimum value.

`In the improved electrically insulating pipe section constructed according to the present' invention, the sparking voltage is never lower than the direct current voltage of' the rectifier under practical conditions, even in the case yof a deterioration of the vacuum. This effect is achieved by the arrangement o'f apertured screens fitted airtight in the interior of the insulating pipe section.

Fig. 3 shows a portion of the vacuum pipe line in the interior of which is situated a screen d with a screen aperture 0.

If the screen is made for instance, of' thin sheet metal, it offers practically no resistance to a gas iowing in the pipe section it the mean free length of the path 'of the gas molecules is great, or at least equal to the diameter of the pipe section. This is the case for vacua which exist in the rectifier in normal workings. The interposition of one or more screens therefore does not increase the resistance to the gas current, but nevertheless it has the result Iof preventing the f electrons from passing freely through the pipe section. The effect of this however is that the interposition of the screens reduces considerably the sparking voltage.

The improved electrically insulating pipe section according to the present invention consists of an electrically insulating pipe section in high-vacuum pipe lines in the interior of which said pipe section thin screens are inserted, having their apertures lik;

lll)

stafggered relatively to one another. When in this improved construction, an electron moves in a direction parallel to the aXis oi the pipesection through an aperture in a screen, it does not pass directly into the aperture of the following screen, but impinges with great velocity against the wall of the neXt screen, whereby it loses a large part of its kinetic energy.

A practical embodiment of this invention is illustrated in Fig. 4 in which 0 is the electrically insulating pipesection, Z1 Z9 are screens.- e are annular insets of insulating material, provided for the purpose of spacing the screens d1, cl2, (Z3 apart.

The apertures 01, 02, om 04 in these screens are -arranged eccentrically. The odd-numbered apertures 01, 03, o5 and the even-numbered apertures 02, 04, o6 are arranged respectively in straight lines parallel to the axis of the pipe section, but are arranged 180o apart. Any electron which attempts to travel from a to Z), must take the Zig-zag path through the apertures 02, o3

This means on one hand a lengthening of the path to be traversed by the electrons, whilst on the other hand the kinetic energy of the electron is used up by the repeated impacts against the screens, thereby greatly reducing the impact-ionization of the electrons striking the elect-rode.

The pipe section c may be made of porcelain, glass or other suitable insulating material, and it is made tight against highvacuum by clamping between the two v flanges aand o. The length of this insulating pipe section 1s made such as to provide the necessary creeping surface for preventing an injurious glow discharge at atmospheric pressure. The screens d are preferably made of conductingfg material and set at very short distances apart from one another. They may likewise be insulated from one another, and they should be made to it as far as possible gas-tight against the inside surface of the insulating pipe section.

What I claim is l. In an electrically insulating pipe section for interposition in a high-vacuum pipe line, the combination with a tubular pipe section composed of electrically insulating material connecting in a gas-tight manner the two pipe line sections to be electrically insulated from each other, of a plurality oi thin screens each with an aperture, located in the interior of said insulating pipe section, the aperture in each screen being located out of line with the apertures in the neXt screen on either side.

2. In an electrically insulating pipe section for interposition in a high-vacuum pipe line, the combination with a tubular pipe section composed of electrically insulating material connecting in 'a gas-tight manner the two pipe line sections to be electrically insulated from each other, of a plurality of thin screens each with an eccentrically lo cated aperture, located in the interior of said insulating pipe section, said aperture in each screen being located o out of line with the aperture in the neXt screen on either side.

In testimony whereof I have signed my name to this specification.

vWAULER DLLENBAGH. 

